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The Energetics of Ethanol: An Introduction and Link to Studies

Stacy Mitchell
Institute for Local Self-Reliance
May 12, 2009

Does it take more energy to make ethanol than is contained in ethanol? That question continues to haunt the ethanol industry even after nearly 30 years of expanding production. Over the years more than 20 scientific studies have examined the question. This document contains links to the major studies of the subject completed during the last decade or so.

Some introductory comments may be in order.

First, any analysis should be viewed as an historical snapshot. Virtually all studies of ethanol before 1990 showed a net energy loss. Virtually all of the studies after 1990 show a net energy gain. This is because the ethanol industry, in terms of energy use per gallon of ethanol produced, has become much more efficient over the years, as has the farmer, in terms of energy use per bushel of corn grown.

Second, agricultural productivity and energy intensity varies dramatically not only by crop but by state and even within a state. For example, irrigated corn acreage, which comprise a small percentage of overall corn acreage, is energy intensive. A rotational corn cultivation in which corn fields become soybean fields become alfalfa fields on a three year basis, are low energy users per bushel grown.

The Institute for Local Self-Reliance's own study may be a good starting point because it is very accessible, explains the assumptions used and why, and offers three different scenarios(national average, best current, best near term future). Although completed in 1992 and updated in 1995, we're pleased to say that our conclusions are very much within the range of more recent estimates. Click here for ILSR's 1995 study, How Much Energy Does It Take to Make A Gallon of Ethanol?

The United States Department of Agriculture has done the best job of showing comparative data of all the major studies on the energetics of ethanol. This is an excellent place to understand why there are differences. The initial USDA report was done in 1995. Click here for the 1995 USDA study. An update was published in 2002. Click here for the 2002 USDA study.

David Pimentel, a Cornell University professor, has been ethanol's most consistent critic. He has done several studies over the last few years. His latest was published in 2003. Click here for Pimentel's study. For a more recent critical analysis, see University of California Berkeley professor Tad Patzek's study, Thermodynamics of the Corn-Ethanol Biofuel Cycle (2004).

There have been several critiques of Pimentel's methodology and numbers. Here is a brief one - Click here for the study and critique of Pimentel's work. Another much more extensive, indeed exhaustive, analysis is available here. Click here for study. To my knowledge, Pimentel has not responded to his critics nor done a detailed critique of studies that come to different conclusions.

Pimentel and Patzek teamed together and released a study in March 2005 titled, "Ethanol Production Using Corn, Switchgrass, and Wood; Biodiesel Production Using Soybean and Sunflower," published in the Natural Resources Research journal. Indeed, this latest study reached a remarkable and highly provocative conclusion: the energetics of making ethanol from switchgrass or wood are considerably worse than for making ethanol from corn, and the energetics of making biodiesel from soybeans or sunflowers may be more bleak than making ethanol from corn.

In response to these latest numbers from Patzek/Pimental, ILSR prepared the following reponse and critique. The Carbohydrate Economy, Biofuels and the Net Energy Debate - issued August 2005. ILSR presented these findings at an August 23, 2005, presentation at the National Press Club [watch the video].

Argonne National Laboratory also weighed in on the latest claims by Patzek/Pimentel and issued a report titled, The Debate on Energy and Greenhouse Gas Emissions Impacts of Fuel Ethanol (August 2005).

Researchers at the University of California – Berkeley released a study published in the January 27, 2006, issue of the journal Science that shows a positive energy balance for ethanol production. [Click to download their full paper, the six analyses, and supporting research from the UC-Berkeley web site].


Stacy Mitchell is a senior researcher with the Institute for Local Self-Reliance, where she directs initiatives on independent business and community banking. She is the author of Big-Box Swindle and also produces a popular monthly newsletter, the Hometown Advantage Bulletin. Connect with her on twitter and catch her recent TEDx Talk: Why We Can't Shop Our Way to a Better Economy.